United States Patent [19] Lane et 211. 4,613,444 Sep. 23, 1986 [11] Patent Number: [45] Date of Patent: [54] REVERSIBLE PHASE CHANGE COMPOSITIONS OF CALCIUM CHLORIDE HEXAHYDRATE WITH POTASSIUM CHLORIDE [75] Inventors: George A. Lane; Harold E. Rossow, both of Midland, Mich. The Dow Chemical Company, Midland, Mich. [21] Appl. No.: 364,159 [22] Filed: Mar. 31, 1982 [30] Foreign Application Priority Data Apr. 15, 1981 [JP] Japan .............................. .. 56-055719 [51] Int. Cl.4 .............................................. .. C09K 5/06 [52] US. Cl. .................................... .. 252/70; 126/400; 165/10 A; 165/l04.11; 165/104.17 [58] Field of Search ........................ .. 252/70; 126/400; 165/10 A, 104.11, 104.17, DIG. 4 [56] References Cited U.S. PATENT DOCUMENTS 2,706,716 4/1955 Howe et a1. ....................... .. 159/1.l 3,958,101 5/1976 Barabas .. 252/70 4,119,556 10/1978 Chubb ...... .. 252/70 4,272,391 6/1981 Lane et a1. . 252/70 4,272,392 6/1981 Lane et al. . 252/70 4,273,666 6/1981 Lane et al. . 252/70 .. 252/70 [73] Assignee: 4,299,274 11/1981 Campbell ..... .. .. 4,392,971 7/1983 Kimura et al. ...................... .. 252/70 FOREIGN PATENT DOCUMENTS 11357 5/1980 European Pat. Off. ............ .. 252/70 13569 7/1980 European Pat. Off. ............ .. 252/70 2550106 5/1976 Fed. Rep. of Germany . 43387 11/1974 Japan . 70193 6/1976 Japan . 76183 7/1976 Japan . 84386 6/1980 Japan ................................... .. 252/70 38879 3/1982 Japan . 96079 6/1982 Japan ................................... .. 252/70 2001096A l/l979 United Kingdom . 568669 8/1977 U.S.S.R. .............................. .. 252/70 OTHER PUBLICATIONS Chem Abstracts, vol. 86; 123744d, “Composite Heat Preserver”, Japan Kokai 76—l26,980, Nov. 1976. General Chemistry Applications, Week A30, p. 17, “Heat Storing Compsn for Heating Rooms" J5 3070-989, Seki E33. Yoneda, N. et al., “Eutetic Mixtures for Solar Heat Storage”, Solar Energy, Vol. 21, pp. 61-63, 1978. Primary Examiner-John E. Kittle Assistant Examiner—Robert A. Wax [57] ABSTRACT A reversible liquid/solid phase change composition comprising a mixture of hydrated CaCl; and KCl in which the KC] modi?es the semi-congruently melting behavior of CaCl2.61-I2O to the extent that the mixture approaches congruent melting behavior. The composi tion preferably includes nucleating additives to modify and suppress the supercooling properties of the liquid phase of the composition. The composition most prefer ably comprises an admixture of hydrated CaClz and KC] having an amount of NaCl and/or SrC12.6H2O as an additive suf?cient to obtain an effectively congru ently melting mixture. 43 Claims, No Drawings
Transcript
United States Patent [19] Lane et 211.
4,613,444 Sep. 23, 1986
[11] Patent Number:
[45] Date of Patent:
[54] REVERSIBLE PHASE CHANGE COMPOSITIONS OF CALCIUM CHLORIDE HEXAHYDRATE WITH POTASSIUM CHLORIDE
[75] Inventors: George A. Lane; Harold E. Rossow, both of Midland, Mich.
The Dow Chemical Company, Midland, Mich.
[21] Appl. No.: 364,159
[22] Filed: Mar. 31, 1982
[30] Foreign Application Priority Data Apr. 15, 1981 [JP] Japan .............................. .. 56-055719
Chem Abstracts, vol. 86; 123744d, “Composite Heat Preserver”, Japan Kokai 76—l26,980, Nov. 1976. General Chemistry Applications, Week A30, p. 17, “Heat Storing Compsn for Heating Rooms" J5 3070-989, Seki E33. Yoneda, N. et al., “Eutetic Mixtures for Solar Heat Storage”, Solar Energy, Vol. 21, pp. 61-63, 1978.
Primary Examiner-John E. Kittle Assistant Examiner—Robert A. Wax
[57] ABSTRACT A reversible liquid/solid phase change composition comprising a mixture of hydrated CaCl; and KCl in which the KC] modi?es the semi-congruently melting behavior of CaCl2.61-I2O to the extent that the mixture approaches congruent melting behavior. The composi tion preferably includes nucleating additives to modify and suppress the supercooling properties of the liquid phase of the composition. The composition most prefer ably comprises an admixture of hydrated CaClz and KC] having an amount of NaCl and/or SrC12.6H2O as an additive suf?cient to obtain an effectively congru ently melting mixture.
43 Claims, No Drawings
4,613,444 1
REVERSIBLE PHASE CHANGE COMPOSITIONS OF CALCIUM CHLORIDE HEXAHYDRATE WITH
POTASSIUM CHLORIDE
BACKGROUND OF THE INVENTION
Phase change materials (PCM’s) in which the heat of fusion of various hydrated salt compositions is em ployed are well known in the literature. In the ASHRAE Journal of September, 1974, entitled SOLAR ENERGY STORAGE, Dr. M. Telkes evalu ated the thermal, physical and other pertinent proper ties of PCM’s on the basis of economics, applicability, corrosion, toxicity and availability for large scale instal lations. Among the materials evaluated were various salt hydrates and their eutectics including CaCl2.6H2O which undergoes several phase transitions to materials of different crystal structure, i.e. CaCl2.6H2O to CaCl2.4H2O+2HgO at 29° C. When heated to a temperature of above 33'’ C., the
salt CaCl2.6H2O dissolves completely in its water of crystallization. When cooled, formation of four differ ent crystal forms is possible, i.e., CaC12.6H2O and three forms of CaCl2.4H2O. If any of the 4H2O crystals form, the heat of fusion is much less than 46 cal/ gm (CaCl2.6 H2O in substantially pure form undergoes a liquid/solid phase transition at about 30° C. releasing or alternately absorbing about 46 calories of heat per gram). Despite the relatively low cost of CaCl2, the formation of its four different crystal forms was deemed to be disadvan tageous.
Carlsson et al., in Swedish Pat. No. 410,004, claim a method for suppressing the tetrahydrate formation dur ing repeated melting and crystallization of a system based on CaCl2.6H2O. In a comparative study, Carlsson et al., determined that in solutions in the concentration range of from 48 to 53 weight percent CaClg, using CaCl2.6H2O of highest purity, the crystallization‘tem peratures for CaCl2.6H2O and CaCl2.4HgO where such that the solution was incongruently melting and that CaCl2.4H2O crystallized and precipitated out of the solution thus losing its heat storage capacity. By using a solution of the same concentration from CaClg of tech nical grade (Road Salt) containing NaCl and KCl as impurities, the solubility of the tetrahydrate decreased and that of the hexahydrate increased and on repeated melting and crystallization, the precipitation becomes signi?cant and the system again loses its heat storage capacity. Thus, the conclusion can be drawn that the use of technical grade CaClz (Road Salt) results in a poorer performance due to a relative increase in tetra hydrate formation as compared to a system based on high purity CaClg. Carlsson et al., discovered that the addition of one or more compounds, including about 2 weight percent SrCl2.6H2O, increased the solubility of the tetrahydrate and suppressed tetrahydrate formation on repeated melting and crystallization. The amount of addition was found to be dependent upon the amount of impurities present in the system, which in an example using Road Salt was determined to be 2.2 weight per cent. The relative amounts of each impurity in the techni
cal grade salt (Road Salt) was not determined nor was it held to be important to the outcome of the tests con ducted. In fact, the use of Road Salt was found to be less desirable from the standpoint of tetrahydrate formation compared to CaCl2 of high purity. Neither was there any recognition by Carlsson et al., that impurities of
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2 NaCl and KCl in the composition could be bene?cial in reducing tetrahydrate crystal formation in such phase change compositions.
Heat storage compositions are ideally packaged in individual encapsulating means for use in conjunction with solar heating systems. Exemplary of suitable known encapsulating means for the heat storage com positions herein described are water impervious ?lms or foils of plastic/metal laminates. Closed cell plastic foams have also been suggested in which the PCM may be encapsulated within the cells of the foam structure as illustrated in, for example, US Pat. No. 4,003,426. Other useful encapsulating means are concrete, metal or plastic containers, pipes, and the like.
SUMMARY OF THE INVENTION
The invention relates to reversible liquid/solid phase change compositions. More particularly, the invention resides in phase change compositions comprising a mix ture of hydrated calcium chloride and potassium chlo ride in which the KC] modi?es the semi-congruently melting behavior of CaCl2.6HgO to the extent that the mixture approaches, and nearly reaches, congruent melting behavior. In a preferred application the phase change composition also includes the addition of NaCl and/or SrCl2.6l-I2O to further modify the CaCl2.6 HgO/KC] mixture to thereby obtain a composition which is effectively a congruently melting composition. Optionally, the compositions of the invention also con tain select nucleating additives to modify and suppress the supercooling properties of the liquid phase of the phase change compositions. The present invention now recognizes that the addi
tion of a predetermined amount of KCl to hydrated CaClg substantially reduces the formation of crystal forms other than CaCl2.6H2O thereby providing a CaClz/KCI mixture in which the precipitation of crys tal forms other than CaCl2.6HgO on repeated melting and crystallization is substantially reduced. In addition, the hydrated CaClg/KC] composition of the invention still provides a substantial cost advantage over other PCM’s. Although the hydrated CaClg/KCI mixture of the
invention surprisingly reduces the formation of crystal forms other than the hexahydrate form, it was found that it still retained the inherent characteristics of the supercooling properties of CaCl2.6I-I2O. Accordingly, the present invention provides for the addition of select nucleating agents to the mixture thereby substantially improving the supercooling characteristics of the hy drated CaClg/KCl system. The avoidance of supercooling during the crystalliza
tion of hydrated CaClZ, as by the addition of various nucleating agents, is known in the literature. Nucleating agents are substances upon which the phase change material crystal will grow with little or no supercool ing. Accordingly, nucleating agents were not intended as additives to achieve congruently melting salt hy drates. Nucleators for hydrated CaClz systems in partic ular are described in, for example, U.S.S.R. Inventor ship Certi?cate No. 568,669, granted Mar. 3, 1975; Japa nese Pat. No. 969,909, granted Aug. 31, 1979; and US. Pat. No. 4,189,394. The present invention comprises a further improve
ment over the state of the art in that the nucleators of the invention are selective nucleators that will effec
4,613,444 3
tively reduce supercooling in the hydrated CaClg/KCl system of the present invention. Although the addition of less than about 8.0 weight
percent KCl to CaCl2.6H2O effectively reduces the tendency of the phase change composition to form, on freezing, the undesired phase CaCl2.4H2O, even this amount is not quite sufficient to prevent completely the formation of CaClgAHgO. Accordingly, in a preferred embodiment of the invention, the formation of CaCl2.4 H2O can be totally prevented from crystallizing if KCl is used in combination with NaCl and/or SrCl2.6H2O. As hereinafter demonstrated, the addition of SrCl3.6H2O to CaCl2.6H2O to the full limit of its solu bility does not prevent crystallization of CaCl2.4H2O during freezing. However, as hereinafter further dem onstrated, the addition of KCl plus NaCl; KC] plus SrCl1.6H2O, or KCl plus NaCl and SrCl2.6H2O modi ?es the phase equilibrium of CaCl2.6H2O to fully su press the crystallization of CaClZAI-IZO.
DETAILED DESCRIPTION OF THE INVENTION
The present invention represents a signi?cant im provement towards the elusive goal of developing an inexpensive reversible liquid/solid phase change com“ position based on hydrated CaClg in admixture with KCl in which the KCl is present in the hydrated CaClz in an amount effective to reduce, during retrieval of the stored heat on freezing of the composition, formation of hydrated CaClZ crystalline phases other than CaCl2.6 H2O. The most basic composition of the invention com prises a mixture of from about 46 to about 52 weight percent CaClg and from about 0.5 to about 8.0 weight percent KCl, with the balance being H2O (in an amount up to 100 weight percent). Preferably, the composition of the invention comprises a mixture of from about 47 to about 51 weight percent CaClz and from about 2.3 to about 6.0 weight KCl with the balance being H2O (in an amount of up to 100 weight percent). Most preferably, the composition of the invention comprises a mixture of from about 48.0 to about 48.5 weight percent of CaClZ and from about 4.0 to about 4.7 weight percent KCl with the balance being H2O (in an amount of up to 100 weight percent).
Effective amounts of the selected nucleating agents for the hydrated CaCIZ/KCI system of the invention are determined by testing a given composition over repeti tive phase change cycles. While the following data illustrate that the nucleating agents produce marked bene?ts, such amounts should preferably not exceed 2.0 weight percent of the weight of the hydrated CaCIZ/KCl mixture. Preferably, the nucleating agents are present in an amount of from about 0.005 to about 2.0 weight percent, based on the total weight of the composition. More preferably, the amount of the nucle ating agents in the phase change composition is from about 0.01 to about 1.0 weight percent and most prefer ably, from about 0.10 to about 0.50 weight percent. It should be understood, however, that when reference is made to the addition of a given percentage of a nucleat ing agent, it is in addition to the amounts of ingredients already present in the phase change composition. Ac cordingly, the existing ingredient percentages are re duced proportionately to accomodate the addition of a nucleating agent(s). Hydrated salt phase change materials exhibit three
general types of phase/change behavior: congruent, semi-congruent and incongruent melting. The most
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4 desirable behavior is congruent melting which occurs when the solid phase change composition (ratio of salt to bound water) is the same as the liquid phase composi tion. In that case, the hydration/dehydration process appears identical to the melting and freezing process. The term “effectively congruently melting mixture”
herein used de?nes a mixture of ingredients, based on aqueous calcium chloride, for which, at the melting point, solid and liquid phases are in stable equilibrium: the solid phase containing no hydrated calcium chloride material other than the hexahydrate or solid solutions thereof; and the liquid phase containing, for every mole of calcium chloride, six moles of water, plus sufficient water to form the stable hydrate of any additive materi als in solution.
Semi-congruent melting occurs when a phase change material has two or more hydrate forms with differing solid compositions and melting points. The material can be transformed into other hydrate forms before either complete melting or freezing occurs, resulting in a broadened melting point range. In addition, there is a temporary loss in thermal storage capacity. Calcium chloride hexahydrate is an example of a semi~congru ently melting phase change material.
Incongruently melting phase change materials yield two distinct phases upon melting: a saturated solution and a precipitate of an insoluble anhydrous salt. If the precipitate settles out of the solution, the anhydrous salt will not hydrate completely upon cooling and some thermal storage capacity will be lost with each freezing /melting cycle. Incongruent melting, as observed with sodium sulfate decahydrate, for example, is a more seri ous problem because it can result in a continual loss of latent heat storage capacity. The term “supercooling” refers to a discrepancy
between the temperature at which freezing initiates and the melting temperature of a given liquid/solid phase change material when cooled and heated under quies cent conditions. The term “additives” includes, in addition to nucleat
ing agents such as have been speci?ed hereinbelow, precursors of such additives which are non-detrimental to the function of the phase change materials of the invention. More particularly, the additives herein re ferred to are either anhydrous or hydrated compositions of inorganic salts or precursor materials which would form the salt upon addition to hydrated calcium chlo ride.
Impurities may be present in the phase change com position in minor amounts of less than 3.0 weight per cent and provided that such impurities do not detrimen tally affect the function of the basic hydrated CaClg/KCl phase change compositions of the invention which may include the hereinafter speci?ed nucleating agents and additives such as NaCl and/or SrCl2.6H2O. Impurities may include, for example, alkaline earth or alkali metal halides such as CaBrg; LiCl; MgClg, or other calcium salts such as CaCOg or CaSO4.
Nucleating agents which have been found to be of particular bene?t in the CaCl2/KCl mixture of the pres ent invention are Ba(OH)2, BaO, Balz, BaS203, BaCO3, BaClz, BaF2, BaF2.HF, Sr(OH)2, SrO, SrCO3, SrF2, S1'I2, or mixtures thereof. Nucleators selected from BaCO3; Baclg; BaO; Ba(OH)2; BaIg; B21504 Sr(OH)2, SrO, or mixtures thereof are preferred.
Compositions containing SrCl2.6H2O as an additive or self-nucleating, unless heated to a temperature suffi cient to dehydrate the SrClg.6H2O. Compositions not
4,613,444 5
containing SrCl2.6H2O as an additive should employ another nucleating additive, unless suitable mechanical means of nucleation are used. The heat storage composition of the invention is pref
erably encapsulated in plastic containers such as the containers sold by Solar Inc., of Mead. Nebr. under the Trade Name SI Suntainer and described in Solar Engi neering of April 1980, page 44. In accordance with the present invention, the reversible liquid-solid phase change composition is hermetically sealed in the encap sulating means to prevent evaporation of water from the composition. The composition comprises an admix ture of hydrated CaClg and KCl, wherein the KC] is added in an amount of less than 8.0 weight percent such that the weight ratio of KCl to CaClg is from 1:50 to 1:5, the balance of the composition is H1O up to 100 weight percent. Preferably, the composition includes one or more nucleating agents in an amount of from about 0.005 to about 2.0 weight percent to reduce supercool ing to 5“ C. or less during retrieval of the stored heat by crystallization. The nucleating agents are selected from Ba(OH)2, BaO, Balg, BaSO4, 13215203, BaCO3, BaClg, BaFz, BaF2.HF, Sr(OH)2, SrO, SrCO3, SI‘F2, SrIZ, or mixtures thereof. The composition may also include impurities in an amount of less than 3.0 weight percent. The following examples illustrate the effectiveness of
KCl for suppressing the formation of unwanted hy drates in the CaCl2.6H2O/KCl phase change composi tions of the invention.
EXAMPLE 1
883 Grams of a stirred liquid aqueous solution of 47.4 weight percent CaClg was allowed to cool until a sub stantial quantity of CaCl2.6H2O crystals was formed in the solution. 8.3 Grams of powdered KCl was then added and allowed to dissolve. When equilibrium was established (at 27.85“ C.), an aliquot of the liquid phase was analyzed and found to contain 47.05 weight percent CaClg and 0.95 weight percent KCl. Stepwise additions of a liquid aqueous solution of 55 weight percent CaClz and powdered KCl were then made, allowing the sys tem to come to equilibrium after each addition.
After 607.9 g of a 55 weight percent CaClZ solution and 4.4 powdered KCl had been added, and equilibrium was established at 29.02“ C., an aliquot of the liquid phase showed 49.32 weight percent CaClg and 0.96 weight percent KCl. Optical Microscopy showed only hexagonal CaCl2.6H2O in the suspended solid phase.
After an additional 101.8 g of a 55 weight percent aqueous CaClz and 1.2 g powdered KCl was added, the equilibrium temperature was 29.35“ C., and the liquid phase contained 49.29 weight percent CaClg and 0.95 weight percent KCl. Optical Microscopy showed only the triclinic crystals of CaClgAHgO in the suspended solid phase.
Further additions of 55 weight percent aqueous CaClg and powdered KCl showed that for a composi tion with a weight ratio of KChCaClg being 1:50, and a mole ratio of HgOzCaClz being 6:1, the equilibrium melting point of CaCl2.4H2O is 32.1“ C., and of CaCl2.6 H3O (extrapolated) is 29.2“ C. Thus, a melted CaCl2.6 H2O sample with the above composition, if cooled, must cool through a temperature span of 2.9“ C., during which crystallization of CaCl2.4H2O is possible, before freezing of CaCl2.6H2O can begin.
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EXAMPLE 2
In the same manner as in Example 1, 932 g of 46.0 weight percent aqueous CaClg and 20.69 g powdered KCl were brought into equilibrium with solid CaCl2.6 H2O at 25.85“ C. The liquid phase contained 45.28 weight percent CaClg and 2.46 weight percent KC].
Stepwise addition of 55 weight percent aqueous CaClz and powdered KC] resulted in a slurry of solid CaCl2.6H2O in equilibrium at 28.13“ C. with a solution containing 48.73 weight percent CaCl; and 2.64 weight percent KCl. The further addition of 55 weight percent CaClg gave an equilibrium slurry (28.70“ C.) of CaCl2.4 H2O in a solution with 48.98 weight percent CaClz and 2.43 weight percent KCl.
Further additions of concentrated CaClZ solution and powdered KC] showed that for a composition with a weight ratio of KClzCaClZ being 1:20, and a mole ratio of H2O:CaCl2 being 6:1, the equilibrium melting point of CaCl2.4H2O is 30.1“ C., and of CaCl2.6H1O (extrapo lated) 28.1“ C. A melted CaCl2.6H2O sample of the above composition, in freezing, must cool, therefore, through a temperature span of 2.0“ C., during which crystallization of CaCl2.4H3O is possible, before freez ing of CaCl2.6H1O can begin.
EXAMPLE 3
In the same manner as in Examples 1 and 2, 889 g of 44.0 weight percent aqueous CaClg, saturated with KCl, was brought into equilibrium with solid CaCl2.6H2O at 24.52“ C. The liquid phase contained 44.16 weight per cent CaClg and 3.16 weight percent KCl.
Stepwise addition of an aqueous solution of 53.7 weight percent CaCl; 1 and 2.6 weight percent KCl, supplemented on occasion with powdered KCl, re sulted in a slurry of solid CaCl2.6H2O and KCl in equi librium at 27.26“ C. with a solution containing 4821 weight percent CaClg and 4.19 weight percent KCl. Further addition of the 53.7/2.6 weight percent CaCl2/KCl solution and powdered KC] yielded a slurry of solid CaClgAHgO and KCI in equilibrium at 27.91“ C. with a solution analyzing at 48.21 weight precent CaClz and 4.48 weight percent KCl.
Further additions of the concentrated CaClg/KCl solution and solid KCl showed that below a mole ratio of about 5.921, H2OIC3C12, KCl is completely soluble, if a weight ratio of KClzCaClz of 1:10 is maintained. At a 6:1 mole ratio of HgOzCaClg and a weight ratio of KChCaClg of 1:10, the equilibrium melting point of CaCl2.4H2O is 28.0“ C., and of CaCl2.6H2O, 27.3“ C. A lique?ed sample of CaC12.6H2O of this composition, in freezing, must cool through a span of only 0.7“ C., dur ing which crystallization of CaCl2.4H2O is possible, before freezing of CaCl2.6I-I2O can occur.
EXAMPLE 4
In the same manner as in Examples 1, 2 and 3, a sam ple of aqueous CaClg was studied, without the addition of any KCl. At a mole ratio of 6:1, HgOzCaCb, with no KCl present, the equilibrium melting point of CaCl2.4 H2O is 32.8“ C., and of CaCl2.6H2O is 29.60 C. Thus, a melted sample of CaCl2.6H2O, in cooling, must pass through a span of 3.2“ C., during which CaC1g.4H2O crystallization is possible, before CaCl2.6H2O freezing can begin.
4,613,444 '7 8 TABLE I
Effect of Potassium Chloride on Calcium Chloride Hydrate Phases”
KCl/CaClg CaCIZAI-IZO CaCl3.6I-lg0 cac12.4H20 Max. Amt. wt. ratio m.p., “C. mp, °C. Stable Span CaClZAI-IZO
ob 32.8 29.6 3.2" c. 9.45% 150 32.1 29.2 2.9“ C. 7.58% 120 30.1 28.1 2.0“ C. 5.88% 1110 28.0 27.3 0.7" c. 1.86%
“6:1 mole ratio HgOzCnCI; hNol an example of the invention - Example 4
m.p. — melting point
Table I summarizes the ?ndings of Examples 1-4 as to the equilibrium melting points of the tetrahydrate and hexahydrate of CaClg. 15
Table I also shows the maximum theoretical amount _ of CaCl2.4H2O that could be formed in the freezing TABLE n'commued process. This was calculated using the “lever princi- Supercooling, °C., Average ple”, from the peritectic compositions determined in the Nucleator KChCaClz KChCaClz experiments outlined in Examples 1 to 4. It was surpris- 20 Compound Wt. % No KCl” 120 1.10 ingly found that the addition of KCl not only reduces " 0,05 ()_55 __ _ the temperature span within which CaC12.4H2O can be " (101 L92 — - formed, but that it also reduces the maximum theoreti- " 0005 4'45 7-5 —
. BaO 1.00 - 0.7 >11 cal conversion of the CaCl1.4H2O crystal form. ., 0.05 __ 2.25 12
In practice, less than the theoretical amount of 25 I’ (110 Q_4() _ __
CaCl2.4H3O is obtained. Both supercooling and slow " 0-05 L45 — ——
crystal growth rate mitigate against tetrahydrate forma- B"I (1)82) 12.0 1-6 _1 tion. For example, a composition of Example 3 contain- a 2 0:50 : 3:9 ing 48.22 weight percent CaClZ, 4.82 weight percent " 0.10 0 _
KCl, and 49.96 weight percent H2O would yield no 30 " 0-05 0~4 — — CaClgAHgO whatsoever, if the tetrahydrate super- " Om 4-7 -
. , BaSO4 1.00 — 7.7 >16 cooled as little as 0.7 C. and the hexahydrate were H 0.50 _ 80 17]
nucleated so as not to supercool. Further, in the experi- " 0.10 0.26 _ _ ments described in Examples 1, 2 and 3 above, it was " 0.05 7.4 - _
noted that whenever CaClZAHZO crystals were pres- 35 M903 5-28 ‘7 i-g >1; ent, upon each addition of concentrated CaCl; solution, H 0:10 0' ' I: a much greater time period was required for tem- " 0,05 0 _ _
perature/ composition equilibrium to be established than " 0-01 0-1 —— — was the case in Example 4 which did not contain KCl. " O-OOS 6-0 '_ _
This illustrates the slow rate of CaCl2.4H2O formation. 40 B892 (1)228 0* 1kg " 0.10 1.03 - -
EXAMPLE 5 .. Om L38 _ _
In order to determine the effects of nucleating agents on hydrated CaCl2/KCl heat storage materials, a num ber of 80 gram samples of CaCl2.6H2O were prepared with varying levels of KCl added to the CaCl2.6H2O. Selected nucleating agents were added to the hydrated CaClQ/KCl mixture to study their effects on supercool mg. For comparison, a control sample was prepared with
out the addition of a nucleating agent to the hydrated CaCh/KCI storage material. The control sample con tained 48.2 weight percent CaClg; 4.8 weight percent KCl and 47.0 weight percent water. In 4 of 10 freeze thaw cycles, the control sample completely failed to freeze. In the remaining 6 cycles, an average supercool ing temperature of greater than 14° C. was detected. The results of the effect of KCl on barium salt nuclea
tors for CaCl2.6H2O are summarized in Table II.
TABLE II Supercooling, °C., Average
Nucleator KClcCaClz KCl:CaCl2 Compound Wt. % No KCl’J 1:20 1:10
None” — — — >14
Ba(OI-I)2 2.00 — — 2.5
" 1.00 — 0.3 4.9
' " 0.50 0.0 0.25 9.5
" 0.10 0.16 —— —
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"Not an example of the invention.
From Table II, it is evident that, in the absence of KCl, the amount of supercooling decreased as the level of the barium salt nucleator was increased. At a level of 0.5 weight percent, no supercooling was observed. In the case of BaCO3 substantially no supercooling was observed at a level as low as 0.01 weight percent. For example containing KCl, the effectiveness of the nucle ators diminished and a higher level of supercooling was observed as the KCl level was raised. Accordingly, it is evident from the data that higher levels of nucleators must be added in the presence of KCl to control super cooling. In general, depending on the barium salt se lected as the nucleator, it is desirable to add at least 0.5 weight percent when the ratio of KCl:CaCl2 is 1:20. When the ratio of KCl:CaCl2 reached 1:10, it was found that the addition of a nucleator at that level produced no further bene?ts in reducing the level of supercool ing. It would therefor be impractical to rely solely on any one of a select barium salt or barium salt mixture to control supercooling at a KCl:CaCl2 ratio of 1:10 or greater. The effects of strontium salt nucleators on the hy
drated CaClZ/KCl composition of the invention are illustrated in Table III.
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TABLE III
Effect of KCl on Strontium Salt Nucleators for CaCl7.6l~l-1O
supercooling, °C., Average Nucleator KClzCaClg KCl:CaCl3
Compound Wt. % N0 KCl 1.20 1=10
None —— -— — > 14
SrClg 2.00 —— — 0.1
" 1.00 0 -— —
0.50 6.3 -— —
" 0.10 > 15 —~ —
Sr(OH)2 0.50 0 0 0 " 0.10 0.95 —
0.05 - -—— —
0.02 15.85 5.55 —
Table III illustrates that at the 2.0 weight percent level of SrClg, the amount of supercooling can be re duced nearly to zero, even in the presence of the maxi mum level of KCl. In the case of Sr(OH)2, the addition of 0.5 weight percent surprisingly eliminated supercool ing completely, even at the highest ratio of KCl:CaCl2 of 1:10.
Table IV shows the combined effect of barium salts and strontium salts on supercooling of hydrated CaClz and KCl heat storage compound.
TABLE IV
Combined Effect of Binary Nucleators on CaCl7.6H1O
supercooling Average. °C. Nucleator No 1<c1<a1 KChCaClmSrClv
(“Not an example of the invention (")Assumed to be 0. since the lower level of nucleator yielded 0' supercooling mNaClzCaClg (moo).
From Table IV, it will be noted that the presence of the binary barium/strontium salt nucleator had the un expected property of suppressing supercooling even in the presence of a high level of KCl. Very little differ ence was observed between the results for nucleated pure CaCl2.6H2O and nucleated CaCl2.6I-I2O contain ing KCl and SrClZ. Since KCl is known to reduce the effectiveness of barium salts, the lack of supercooling can be attributed to the action of SrClg in reversing the effect of KCl on nucleators.
Table V illustrates the most effective combination of barium salt or strontium salt nucleators, or mixtures thereof, and weight percentages on supercooling of KCl/CaClZ mixtures at ratios of 1:20 and 1:10.
TABLE V
Nucleator(s) supercooling. °C., Average Weight KCl:CaCl3 = KClzCaClg =
Compound Percent 1:20 1:10
Ba(Ol-l)3 0.5 0.25 BaO 1.0 0.7 BaO 0.5 0.0 SrClg 0.5
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10 TABLE V-continued
Nucleator(s) supercooling, °C.. Average Weight KClzCaClg = KClzCaClZ =
From Table V, it will be seen that the addition of BaIg suppresses supercooling to 16° C. and although higher than the remaining listed nucleators, still repre sents a highly effective material. Surprisinly, the mix ture of Balz with SrClg suggests a synergistic effect since 0° C. supercooling was obtained.
EXAMPLE 6
The following Example involves saturation of CaCl2.6H2O with NaCl. It shows that there is but a slight effect on the potential formation of tetrahydrate from this additive alone.
In the same procedural manner as in Example 2, 1230 g of a 47.47 weight percent aqueous CaClg solution and 12.4 g NaCl powder were mixed and brought to equilib rium with solid CaCl3.6H2O at 28.13° C. The liquid phase contained 47.28 weight percent CaClg, 52.43 weight percent H20, and 0.29 weight percent NaCl by analysis.
Stepwise addition of an aqueous solution of 55.15 weight percent CaClg resulted in a slurry of solid CaCl2.6H;O and NaCl in metastable equilibrium at 29.40” C. with a solution of 49.92 weight percent CaClg, 49.84 weight percent H20, and 0.24 weight percent NaCl, by analysis. Further addition of the 55.15 weight percent solution of CaClg yielded a slurry of solid CaCl2.4l-I2O and NaCl in equilibrium at 31.48“ C. with a solution of 50.14 weight percent CaClg, 49.60 weight percent H20, and 0.26 weight percent NaCl.
Further additions of the concentrated CaClg solution showed that at a 6:1 mole ratio of H1O:CaCl2, saturated with NaCl, the equilibrium melting point of CaCl3.4 H2O is 32.8“ C., and the metastable equilibrium melting point of CaCl2.6H1O is 294° C. A lique?ed sample of CaCl2.6H2O of this composition, in freezing, must cool through a span of 3.4° C., during which the crystalliza tion of CaClgAHgO is possible, before freezing of CaCl2.6H2O can begin. Thus, saturation with NaCl causes a slight increase in the tendency to form tetrahy drate.
EXAMPLE 7
This Example involves saturation of CaCl2.4H2O with both KCl and NaCl, and it is an example of the present invention. It shows that although NaCl addition causes a slight increase in CaCl2.4H2O formation, and KCl addition markedly reduces, but does not eliminate CaCl2.4H2O formation, the combination of KC] and NaCl additives totally suppresses tetrahydrate forma tlon.
In the same procedural manner as in Example 2, 898 g of a mixture of 46 weight percent CaCIZ, 47 weight percent H20, 6 weight percent KCl, and 1 weight per
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cent NaCl was heated, cooled, and brought to equilib rium at 26.02° C. CaCl2.6H2O, KCl, and NaCl crystals were in equilibrium with a solution of 45.65 weight percent CaCl2, 49.5 weight percent H2O, 3.9 weight percent KCl, and 9.95 weight percent NaCl.
Stepwise addition of an aqueous solution of 53.0 weight percent CaClg, 5.5 weight prcent KCl, and 41.5 weight percent H2O resulted in a slurry of CaC12.6H2O in equilibrium at 26.90° C. with a solution containing 47.90 weight percent CaCl2, 46.6 weight percent H2O, 4.7 weight percent KCl, and 0.83 weight percent NaCl. Further addition of the 53.0/5.5 weight percent C?Clg/KCI solution and 5 g powdered NaCl yielded a slurry of CaClZAI-IZO in equilibrium at 27.82° C. with a solution’ analyzing 48.15 weight percent CaCl2, 46.2 Weight percent H3O, 4.8 weight percent KCl, and 0.86 weight percent NaCl.
Further addition of the concentrated CaClg/KCI solution, powdered NaCl, and powdered KCl demon strated that at a 6:1 mole ratio of H2O:CaCl2, saturated with KCl and NaCl, the equilibrium melting point of CaCl2.6H2O is 27.0° C., and the metastable equilibrium melting point of CaCl2.4H2O is about 26.7” C. A lique ?ed sample of CaCl2.6H2O of this composition, in freez ing, will crystallize to solid CaCl2.6H2O, without the possibility of CaCIZAI-IZO formation.
EXAMPLE 8
This Example is not an example of the invention and demonstrates that CaCl2.6H2O saturated with SrCl2.6H3O decreases but cannot eliminate the poten tial for tetrahydrate formation.
In the same procedural manner as in Example 2, 748 g of a mixture of 45 weight percent CaClg, 53 weight percent H20, and 2 weight percent SrCl; was heated, cooled, and brought to equilibrium at 25.91° C. Crystals of SrCl2.2H3O and CaCl2.6H2O/SrClg.6H2O solid solu tion were in equilibrium with liquid analyzing 44.18 weight percent CaClg, 55.37 weight percent H20, and 0.55 weight percent SrClz.
Stepwise addition of a solution of 54.3 weight percent CaClg, 43.7 weight percent H20, and 2.0 weight per cent SrCl2 resulted in a slurry of CaCl2.6H2O/SrCl2.6 H2O solid solution and SrCl2.2H2O crystals in metasta ble equilibrium at 30.28’ C. with liquid analyzing 50.08 weight percent CaClg, 49.22 weight percent H20, and 0.70 weight percent Sl'Clz.
Further stepwise addition of concentrated CaClg/SrClg solution, followed by cooling, resulted in a slurry of CaCl2.4H2O and SrCl2.2H2O in equilibrium at 30.50° C. with liquid analyzing 49.70 weight percent CaClg, 49.66 weight percent H20, and 0.50 weight per~ cent SrCl2.
Further experiments of this type showed that at a mole ratio of 6:1 of H2O:(CaCl2-|-SrClZ), the equilib rium melting point of CaCl2.4H2O is 32.1” C., and the metastable equilibrium melting point of a CaCl2.6H2O (solid solution) is 304° C. A lique?ed sample of CaCl2.6H2O of this composition, in freezing must cool through a span of 1.7“ C., during which CaCl2.4H2O can freeze, before crystallization of CaCl2.6H2O can begin. Thus, SrCl2.6H2O additive reduces the tendency of the tetrahydrate to form (roughly by half), but does not prevent it entirely.
EXAMPLE 9
The following example involves the saturation of CaCl2.6H2O with both KCl and SrCl2.6H2O, and is an
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112 example of the present invention. This Example demon strates that the addition of both KCl and SrCl2.6H2O to CaCl2.6H2O totally reduces tetrahydrate formation.
In the same procedural manner as in Example 2, 757 g of a mixture of 43.4 weight percent CaClg, 4.3 weight percent KCl, 1.9 weight percent SrClg, and 50.3 weight percent H2O was heated, cooled, and brought to equi librium at 27.l8° C. Crystals of KCl, SrCl2.2H2O and CaCl2.6I-I2O/SrCl2.6H1O were in equilibrium in a liq uid which was analyzed to contain 44.21 weight percent CaClZ, 3.9 weght percent KCl, 1.15 weight percent SrClg, and 50.7 weight percent H2O.
Stepwise addition of a solution containing 51.7 weight percent CaClg, 5.2 weight percent KCl, 1.0 weight percent SrClg and 42.2 weight percent H2O led to a slurry of CaCl2.6H2O/SrCl2.6H2O solid solution, SrCl2.2H2O and KC] crystals in equilibrium at 27.68" C. The liquid was analyzed to contain 47.57 weight per cent CaCl2, 47.02 weight percent H2O, 4.65 weight percent KCl, and 0.76 weight percent SrCl2.
Further stepwise additions of concentrated CaCIZ/KCI/SrClZ solution, followed by cooling, led to a slurry of CaCl2.4H2O, SrCl2.2H2O, and KCl in equi librium at 27.54° C. The liquid was analyzed to contain 48.03 weight percent CaClg, 46.45 weight percent H2O, 4.9 weight percent KCl, and 0.62 weight percent SrCl2.
Further experiments of this type showed that at a mole ratio of 6:1 of H2O:(CaCl2+SrCl2), the equilib rium melting point of CaCl2.6H2O (solid solution) is 27.8° C., and the metastable equilibrium melting point of CaCl2.4HgO is about 27° C. A lique?ed sample of CaCl2.6H2O of this composition, in freezing, will crys tallize to crystalline CaCl2.6H2O/SrCl2.6H2O solid solution without the possibility of tetrahydrate forma tion.
EXAMPLE 10
This Example illustrates saturation of CaCl1.6H2O with KCl, SrCl2.6H1O, and NaCl, and is an example of the present invention. Since tetrahydrate crystallization in CaCl2.6H2O can be suppressed by adding KCl-l-SrClZ or KCl+NaCl, but not SrCl2+NaCl, this Example surprisingly demonstrates that addition of all three salts would be bene?cial in completely suppress ing the tetrahydrate formation.
In the same procedural manner as in Example 2, 761 g of a mixture of 43.16 weight percent CaClg, 49.52 weight percent H2O, 4.37 weight percent KCl, 1.96 weight percent SrClg, and 0.99 weight percent NaCl was heated, cooled, and brought to equilibrium at 26.62“ C. Crystals of CaCl2.6H2O/SrCl2.6H2O, SrCl2.2I-I2O, KCl, and NaCl were in equilibrium. The liquid was analyzed to contain 43.98 weight percent CaClg, 50.78 weight percent H3O, 3.90 weight percent KCl, 1.02 weight percent SrClg, and 0.32 weight per cent NaCl.
Stepwise addition of a solution containing 51.8 weight percent CaClg, 41.5 weight percent H2O, 5.2 weight percent KCl, 1.0 weight percent Sl'Clg, and 0.5 weight percent NaCl led to a slurry of CaCl2.6 H2O/SrCl2.6H2O, SrCl2.2H2O, KCl, and NaCl in equi librium at 27.56" C. The liquid was analyzed to contain 47.52 weight percent CaCl2, 46.62 weight percent H2O, 4.75 weight percent KCl, 0.83 weight percent SrClg, and 0.28 weight percent NaCl.
Further stepwise addition of the concentrated CaClg/KCl/SrClg/NaCl solution led to a slurry of CaCl2.4H2O, SrCl2.2H2O, KCl, and NaCl in equilib
4,613,444 13
rium. The liquid was analyzed to contain 48.48 weight percent CaClg, 45.68 weight percent H3O, 5.33 weight percent KCl, 0.84 weight percent SrCl1, and 0.26 weight percent NaCl, at a temperature of 27.77° C. At a mole ratio of 6:1 of H2O:(CaCl2+SrCl2), the
equilibrium melting point of CaCl2.6I-I2O (solid solu tion) is 27.5° C., and the metastable equilibrium melting point of CaCl2.4HgO is about 26° C. A lique?ed sample of CaCl2.6H2O of this composition, in freezing, will crystallize to solid CaCl2.6H2O/SrCl2.6H2O solid solu tion without the possibility of tetrahydrate formation.
Table VI summarizes the results of previous Exam 3 ples 3 and 4 and new Examples 6 through 10 and the
effects of additives on calcium hydrate phase at a 6:1 mole ratio, H2O:(CaCl2+SrCl2), saturated with the indicated additive(s).
TABLE VI Effect of Additives on Calcium Chloride Hydrate Phases
CaClZAHZO CaClg.6HgO CaCl2.4l-IgO Additive mp, °C. m.p., 'C. Stable Span
As a further demonstration of the elimination of CaCl2.4I-I2O formation by the present invention, and as a comparison with other means of tetrahydrate supres sion, a number of CaCl1.6H2O compositions with addi tives were prepared. These samples were melted, and cooled to a temperature barely above the melting point of CaCl2.6H2O, as determined by the experiments in the preceding Examples. After a period of equilibration, a seed crystal of CaCl2.4H2O was added, and its effect observed. If formation of tetrahydrate were possible for these compositions, the seed crystal would persist or grow. Otherwise, it would dissolve. The results of these experiments are illustrated in Table VII in which the CaClgAHgO seeding was conducted at a 6:1 mole ratio of H2O:(CaCl2+SrCl2), saturated with the indicated additive(s). These results con?rm the present invention.
The experiment of Example ll was repeated, using a sample prepared by following the procedures of Swed ish Pat. No. 410,004.
148 Grams of CaCl2.6H2O was prepared, containing 50.66 weight percent CaClg and 49.43 weight percent H2O. Then 2.97 g (2 percent by weight) SrCl2.6H2O was added and dissolved at 60° C. After equilibration at 32° C. for 23 hours, the solution was ?ltered, and the test of Example 11 was performed at 306° C. Seeds of CaClgAHgO grew in the solution. After two days the remaining liquid was found to contain 49.30 percent
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14 CaClg, 50.31 percent H20, and 0.39 percent SrClg by weight, a mole ratio of 6.252:l of H2O:(CaCl2+SrCl2).
This experiment demonstrates that the composition is not a congruently melting composition.
SUMMARY OF EXAMPLES 6 TO 12
As discussed hereinbefore, the addition of SrCl1.6H2O to the full limit of its solubility in CaCl2.6 H2O does not prevent the the crystallization of CaCl2.4 H2O during freezing of such composition. When SrCl2.6H2O is added, the melting point of CaCl2.6H2O increases (due to formation of an isomorphous solid solution), and the melting point of CaClZAHZO de creases. Again, the freezing process is like that for pure CaCl2.6H2O, except that less tetrahydrate can form, and that solid solution freezes in place of the hexahy drate. At the solubility limit of about 1.0 weight percent SrCl2.6H3O, freezing of the tetrahydrate begins at 32.2° C., and the peritectic reaction isotherm is at 30.6“ C. It is estimated that if about 2.1 weight percent SrCl2.6H2O were dissolved, no tetrahydrate could form. However, the limit of solubility is about 1.0 weight percent. Ac cordingly, the effect of SrCl2.6H2O on the freezing of CaCl2.6H2O is as predicted by Carlsson, et al. but be cause of the solubility limit of SrCl2.6H2O their pre dicted results cannot be achieved.
In accordance with the present invention, it has sur prisingly been found that about 0.8 weight percent NaCl can be added to CaClZ.6H2O saturated with KCl. This reduces the melting point of CaCl1.6H1O, but reduces faster the melting point of CaCl2.4HgO. The combined effect of the two additives is to prevent any tetrahydrate formation. The mixture melts at 270° C. The CaCl2.6I-I2O/CaCl2.4I-I2O eutectic point is at 270° C. at the CaCl2.5.98H3O stoichiometry.
In accordance with the invention, it has also been surprisingly found that when KCl is added to CaClg.6 H2O saturated with SrCl2.6H1O, the melting point de creases. That of the tetrahydrate is affected more than that of the hexahydrate. The following data indicate that about 3.25 weight percent KCl will effectively prevent tetrahydrate formation. The solubility limit is about 4.75 weight percent, so that there is no problem in obtaining the necessary concentration. The mixture, saturated with KC] and SrCl2.6H2O, melts at 27.8” C. The hexahydrate/tetrahydrate eutectic point is at 27.6” C. and CaCl2.5.9lH2O stoichiometry.
Further, in accordance with the invention, it has been found that about 4.8 weight percent KCl, plus 0.3 weight percent NaCl, plus 0.8 weight percent S1'Cl2.6H2O are soluble in CaCl2.6HgO and that tetrahy drate crystallization is completely prevented. The mix ture melts at 27.5° C. There is a eutectic point at 27.4° C. at the stoichiometry (CaCl2+SrCl2).5.82H2O.
In Example 4, it was demonstrated that for CaCl2.6 H3O without additives, considerable tetrahydrate for mation is possible during freezing.
In Example 3, it was demonstrated that by saturating CaCl2.6I-I2O with KCl, the potential for tetrahydrate formation is reduced markedly and that KCl surpris ingly modi?ed the semi-congruently melting behavior of CaCl2.6I-I2O to the extent that the mixture nearly reaches congruent melting behavior. What is claimed is: 1. A reversible liquid/ solid phase change composition
comprising an admixture of hydrated CaClz and KCl, wherein KCl is added to the hydrated CaClg in an
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amount suf?cient to modify the semi-congruent melting behavior of CaCl2.6H2O to the extent that the mixture approaches the congruent melting behavior of a con gruently melting mixture and to reduce, during retrieval of the stored heat by crystallization of the mixture, the formation of crystalline CaClz hydrate phases other than CaC12.6H30.
2. The composition of claim 1, comprising from about 46 to about 52 weight percent CaClg having KC] added to the CaClz such that the KCl is present in an amount of from about 0.5 to about 8 weight percent, with the balance being H2O (up to 100 weight percent).
3. The composition of claim 1 or 2, comprising from about 48.0 to about 48.5 weight percent CaCl2, having KCl added to the CaClg such that the KCl is present in an amount of from about 4.0 to about 4.7 weight percent with the balance being H2O (up to 100 weight percent).
4. The composition of claim 1, wherein the weight ratio of KCl to CaClZ in the composition is from 1:50 to 1:5 and wherein the mole ratio of the H20 to CaClZ in the composition is about 6:1.
5. The composition of claim 4, wherein the weight ratio of KCl to CaCl; in the composition is from 1:15 to 1:10.
6. The composition of claim 1, including an amount of NaCl added to the hydrated CaCl; suf?cient to obtain an effectively congruently melting mixture.
7. The composition of claim 6, wherein the weight ratio of NaCl to CaClg in the composition is from 1:40 to 1:70.
8. The composition of claim 7, wherein the weight ratio of NaCl to CaCl2 in the composition is from 1:45 to 1:65.
9. The composition of claim 1 or 6, including an amount of SrCl2.6H2O added to the hydrated CaClz suf?cient to obtain an effectively congruently melting mixture.
10. The composition of claim 9, wherein the mole ratio of H20 to CaClZ plus SrClg in the composition is about 6:1.
11. The composition of claim 9, wherein the weight ratio of SrCl2.6H2O to CaClZ in the composition is from 1:50 to 1:110.
12. The composition of claim 11, wherein the weight ratio of SrCl2.6H2O to CaClZ in the composition is from 1:75 to 1:100.
13. The composition of claim 9, wherein the weight ratio of SrCl2.6I-12O plus NaCl to CaClg in the composi tion is from 1:40 to 1:70.
14. The composition of claim 1, including the addi tion of one or more nucleating agents in said composi tion in an amount of from about 0.005 to about 2.0 weight percent to reduce supercooling to 5° C. or less during retrieval of the stored heat by crystallization.
15. The composition of claim 14, wherein the nucleat ing agent is present in an amount of from about 0.10 to about 1.0 weight percent.
16. The composition of claim 14 or 15, wherein the nucleating agent is selected from Ba(OH)2, BaO, B312, B21504, B85203, BaCO3, BaClz, BaFg, BaF2.HF, Sr(OH)2, SrO, SrCO3, S1'F2, SrIg, or mixtures thereof.
17. The composition of claim 16, wherein the nucleat ing agent is selected from Ba(OI-I)2; BaO; BaI2; BaSO4; BaCOg; BaClg; Sr(OH)2; or mixtures thereof.
18. The composition of claim 1, wherein said compo sition includes impurities in an amount of less thaan 3.0 weight percent.
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116 19. In a reversible liquid/ solid phase change composi
tion comprising a mixture of CaCl2.6H2O/KCl /NaCl/SrCl2.6H2O and impurities in an amount of less than 3 weight percent of the total weight of the compo sition, the improvement comprising the addition of KCl and NaCl in amounts suf?cient to obtain an effectively congruently melting mixture.
20. The composition of claim 19, the improvement comprising from about 46 to about 52 weight percent CaCl2, having KC] added to the CaClg such that the KCl is present in an amount of from about 0.5 to about 8 weight percent with the balance being H2O (up to 100 weight percent).
21. The composition of claim 19, the improvement comprising a weight ratio of KCl and CaClZ in the com position of from 1:50 to 1:5, a weight ratio of NaCl to CaClg in the composition of from 1:40 to 1:70, and a mole ratio of H20 to CaClz in the composition of about 6:1.
22. The composition of claim 19, the improvement comprising the addition of SrCl2.6HgO to the composi tion in an amount suf?cient to obtain a weight ratio of SrCl2.6H2O to CaClg of from 1:50 to 1:110.
23. The composition of claim 19, the improvement comprising the addition of SrCl2.6HgO plus NaCl to CaClz in an amount suf?cient to obtain a weight ratio of from 1:40 to 1:70.
24. The composition of claim 19, the improvement comprising the addition of one or more nucleating agents to said composition in an amount of from about 0.005 to about 2.0 weight percent to reduce supercool ing to 5° C. or less during retrieval of the stored heat by crystallization.
25. The composition of claim 24, the improvement comprising a nucleating agent selected from Ba(OH)2, BaO, Ball, BaSO4, BaS2O3, BaCO3, BaClz, BaFg, BaFgHF, Sr(OH)2, SrO, SrCO3, S1'F2, SrI2, or mixtures thereof.
26. The composition of claim 19, comprising the im provement of adding a suf?cient amount of KCl to CaClg to obtain a mixture of from about 48.0 to about 48.5 weight percent CaClg and from about 4.0 to about 4.7 Weight percent KCl, and water in an amount to obtain a mole ratio of H20 to CaCl; of about 6:1.
27. The composition of claim 19, comprising the im provement of adding SrClg.6H2O in an amount such that the weight ratio of SrCl2.6H2O plus NaCl to CaClg in the composition is from 1:40 to 1:70 and adding one or more nucleating agents in said composition in an amount of from about 0.005 to about 2.0 weight percent to reduce supercooling to 5° C. or less during retrieval of the stored heat by crystallization, said nucleating agents being selected from Ba(OH)2; BaO; B812; BaSO4; BaCOg; BaClg; Sr(OH)2; or mixtures thereof.
28. A heat storage device comprising an encapsulat ing means having a reversible liquid-solid phase change composition hermetically sealed in said encapsulating means to prevent evaporation of water from the compo sition, said composition comprising an admixture of hydrated CaClg and KCl, wherein KCl is added to the hydrated CaClg in an amount of less than 8.0 weight percent such that the weight ratio of KCl to CaCl2 is from 1:50 to 1:5, the balance of said composition being H2O up to 100 weight percent.
29. The heat storage device of claim 28, including an amount of NaCl added to the hydrated CaCl; suf?cient to obtain an effectively congruently melting mixture.
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30. The heat storage device of claim 29, wherein the weight ratio of NaCl to CaClg is from 1:40 to 1:70.
31. The heat storage device of claim 28 or 29, includ ing an amount of SrClg added to the hydrated CaClg suf?cient to obtain an effectively congruently melting mixture.
32. The heat storage device of claim 31, wherein the weight ratio of SrCl2.6H2O to CaClg in the composition is from 1:50 to 1:110.
33. The heat storage device of claim 31, wherein the weight ratio of SrCl1.6H2O plus NaCl to CaClg in the composition is from 1:40 to 1:70.
34. The heat storage device of claim 28, including one or more nucleating agents added to the hydrated CaClz in an amount of from about 0.005 to about 2.0 weight percent to reduce supercooling to 5° C. or less during retrieval of the stored heat by crystallization, said nucle ating agents being selected from Ba(OH)2, BaO, B312, BaSO4, BaS2O3, BaCO3, BaClg, BaFz, BaFgHF, Sr(OH)2, SrO, SrCO3, SrFg, SI‘I2, or mixtures thereof.
35. The heat storage device of claim 28, wherein said composition includes impurities in an amount of less than 3.0 weight percent.
36. A method of storing heat, comprising the steps of preparing a reversible liquid-solid phase change compo sition by admixing hydrated CaClg and KCl, comprising the steps of adding less than 8 weight percent KCl to the hydrated CaClg such that the weight ratio of KCl to CaCl; in the composition is from 1:50 to 1:5 and the balance being water up to 100 percent, introducing the composition into an encapsulating means for use as a heat storage device, and hermetically sealing the encap
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18 sulating means to prevent evaporation of water from the composition.
37. The method of claim 36, including the step of adding to the composition in an amount suf?cient to obtain an effectively congruently melting mixture, wherein the weight ratio of NaCl to CaClg is from 1:40 to 1:70.
38. The method of claim 36, including the step of adding to the composition in an amount sufficient to obtain an effectively congruently melting mixture, wherein the weight ratio of SrCl2.6H2O to CaClg in the composition is from 1:50 to 1:110.
39. The method of claim 36, including the step of adding NaCl and SrClz to the composition in an amount wherein the weight ratio of SrCl2.6H2O plus NaCl to CaClg in the composition is from 1:40 to 1:70.
40. The method of claim 36, wherein the said compo sition includes impurities in an amount of less than 3.0 weight percent.
41. A heat storage material which comprises a com position of CaCl2.6H2O modi?ed for preventing a crys tallization of CaCl2.4H2O and less than about 8.0 weight percent KC] alone or in admixture with a compound selected from the group consisting of NaCl, SrCl1.6H2O and a mixture thereof.
42. The heat storage material of claim 41, wherein said composition modified for preventing a crystalliza tion of CaClgAHgO comprises CaClz hydrate having a water content at a molar ratio of about 4.74 to about 7.17, based on CaCl2.
43. The heat storage material of claim 42, wherein the CaClg hydrate has a water content at a molar ratio of from about 5.93 to about 6.16, based on CaCl2.
* * * I1‘ *
UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION PATENTND. : 4,613,444 Page 1 of 2
DATED : September 23 , 1986
INVENTUR(S) 2 George A. Lane and Harold E . Rossow
It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below: '
Column 4, line 67, "or self-nucleating,‘ should read ——are self-nucleating,——.
Column 5, line 46, "4.4 powdered" should read ——4.4 g powdered——.
Column 6, line 36, I'CaClZ l and 2.6" should read ——CaCl2 and 2.6-—-.
Column 6, line 44, "Weight precent" should read ——weight percent—- . '
Column 7, line 30, "49.96" should read —-46.96—-.
Column 8, TABLE III-continued, line 24, under subheading Wt. Z, "0.05" should read ——O.50—-.
Column 8, line 51, "example" should read ——examplesé-m
Column 11, line 7, "5.5 weight prcent KCl," should read ---5.5 weight, percent KCl,-—‘.
Column 13, line 62, "49.43" should read --49.34—--—.
Column 14, line 9, "'prevent the the crystallization" should read ——prevent the crystallization-—.
UNITED STATES PATENT AND TRADEMARIé OFFICE. CERTIFICATE OF CORRECTION
PATENTNU. 1 4,613,444
DATED
INVENTOMS) I
Page 2 of 2 September 23, 1986
George A. Lane and Harold E. Rossow
It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below: '.
Column 15, line 67, "less thaan" should read —— less than--.
Column 18, Claim 38, line 9, "adding to" should read ——adding SrCl2 to-—.
Signed and Sealed this -
Thirty-first Day of March, 1987
Attest: '
DONALD J. QUIGG
_ Arresting Oj?cer ' Commissioner of Parents and Trademarks
